Investigation On Preparation And Performance Of RAP-steel Slag Composite Asphalt Mixture

The research of high-content regeneration of waste asphalt pavement materials(Reclaimed Asphalt Pavement,RAP)has become a hot spot in the field of highway at home and abroad.However,the development and application of high-content RAP recycled asphalt mixtures are seriously restricted by the unsatisfactory road performance(such as resistance to water damage,fatigue cracking performance,etc.).In this paper,high-content RAP recycled asphalt mixtures are prepared by using antislip and wear-resistant steel slag aggregates,toughened fibers and high-permeability recyclers,which shows good road performance and solves the problem of resource utilization of RAP and steel slag.Firstly,two different regenerants are used to design and prepare the blended asphalt with 40%,50%,60%,70% and 80% of the mass of aging asphalt(extracted from RAP),and the change characteristics of the blended asphalt such as complex modulus and phase angle,GTS,rutting factor,fatigue factor,viscosity,etc.are analyzed when the blended asphalt mixture changes.The creep characteristics and molecular structure characteristics of the blended asphalt are studied.The results show that the performance indexes of the blended asphalt are between the aging asphalt and the new asphalt,and the performance of the aging asphalt is restored to a certain extent by the diffusion and penetration of the regenerant,and the road performance of the blended asphalt decreases significantly when the amount of aging asphalt is more than 70%.Secondly,two different origins of steel slag,mixed with steel wool fiber toughening material,are selected to design and prepare the composite asphalt mixtures with RAP content of 50%,60% and 70% by the equal volume substitution method,respectively.When compared its performance with ordinary basalt aggregate asphalt mixture,the steel slag as aggregate can significantly improve the road performance of asphalt mixture,and the compaction density of RAP-steel slag composite asphalt mixtures is proposed to be at least 96% of the indoor Marshall test density and 92% of the maximum theoretical density.At the same time,the relationship between the road performance of RAP-steel slag composite asphalt mixtures and the performance of the blended asphalt is investigated,and it is found that the road performance of the mixture,such as dynamic stability,shows a positive linear relationship with the viscosity and creep rate of blended asphalt.The correlation model between the road performance of the mixture and the performance of the blended asphalt is established,which can be used to guide the determination of RAP in the recycled asphalt mixture.Then,the relationship between the road performance of RAP-steel slag composite asphalt mixture and the aggregate morphology,fiber mixing ratio and pore distribution is analyzed,and the reason for the difference in the performance of recycled asphalt mixture prepared by steel slag and basalt as new aggregate is comparatively investigated.The distribution of steel wool fibers and voids in recycled asphalt mixture is analyzed by CT scan to investigate the intrinsic mechanism of steel wool fibers on the performance improvement of recycled mixtures,and the optimum interval[6.4%,7.2%] of steel wool fiber content in recycled aggregates is obtained from the quadratic functional relationship between fiber distribution coefficient and fiber distribution rate and the performance index of RAP-composite asphalt mixtures.The bonding performance of asphalt with aggregate is investigated,and it is found that recycled asphalt decreases significantly and the adhesion breaking force increases with the spalling rate of steel slag as new aggregate,which improves the bonding performance between aggregate and recycled asphalt.Finally,the emission pattern of Volatile Organic Compounds(VOCs)from recycled asphalt mastic is studied,which reveals the internal connection between its chemical compositions and VOCs release behaviors.Meanwhile,the variation law of VOCs emission of recycled asphalt mixture during the mixing process is studied.When the RAP mixtures are 50%,60% and 70%,the VOCs release decreased by 50.30%,82.73% and 94.82%,respectively,which shows that the application of RAP-steel slag composite asphalt mixture is important for the emission management of volatile organic compounds(VOCs).